Playing Eradan
When the AI controls Eradan, it generally does so using ranged combat. He doesn't move forward unless the enemy is at long range and/or stays there to shoot, in which case he moves forward slowly while firing. The biggest advantage in having the AI control Eradan is that the AI won't run out of arrows.
Quite quickly an AI Eradan picks up Evasion and uses it to stand off and keep shooting. This tactic works well for the AI because the AI does not typically run out of ammunition, and the AI can shoot much better than you can: It has a much shorter target acquisition time and typically notices enemies long before you do. It does not, however, always take into account barriers and you will often see it shooting at faraway targets to which it's arrows don't have line of sight, such as a wall or when the AI is at the bottom of a slope or staircase.
Because Eradan stays at range, his damage output is only moderate compared to the carnage you can inflict in melee by controlling him. In the early game he gets Evasion and uses it often to run away from trouble, and that also reduces his usefulness. Of the three character choices, controlling Eradan yourself probably has the biggest impact, especially as you will then definitely have two characters in melee (your Eradan and the AI Farin), which means a lot of damage being dished out.

When you play Eradan, Andriel remains at range. Farin also has to hang back a bit because the AI cannot lead the party -- it can only follow your controlled character. So Farin also starts at range, but will not back away and will switch to melee once an enemy gets close enough.
Farin will eventually take Taunt and use it early when enemies come into range, but in the early game (until around level 10) you will probably draw enemies first so you will be forced to melee, else lose valuable time and XP repositioning.
Melee combat can result in traffic jams with Farin blocking your way sometimes, so try to fan out away from him or immediately move to one side and hack your way back toward the party. You cannot always reliably dodge through allies, and they will block you from executing a critical strike (which can start with a bit of distance as you automatically rush the target) if they are directly in between you and the target.

If you stay in melee, then Andriel is your only ranged character, which isn't bad because two melee characters can take a lot of pressure off her. She will, however, move toward injured characters (when they shout a warning, like Farin's "I'm almost done for!") to erect a healing Sanctuary bubble.

Playing Eradan as an archer is trickier and tends to result in less XP because it's harder to score a headshot or bullseye for those bonuses than it is to score critical hits and final blows, especially when these can put you in Hero Mode and give you an XP multiplier for a Hit Streak. Also, with archery you will need to kill enemies by attrition, and something like a troll (which can survive a 2000-damage stab to the eye) can have more health than you have arrows.

In the mid to late game, once Eradan gets Elusive Foe to a decent duration, he becomes scary powerful. We finished Normal difficulty with Eradan and Dual-Wielding using NO potions EVER and NO Elf-Stones.

Skills

Evasion - Temporarily evade enemy sight.

At a basic level, this doesn't last very long and is inferior to dodging your way out of trouble because it is very easy to interrupt powers. Get it but don't use it until you get some skills for it.

If you are manning a ballista, it does not cancel Evasion.

Does NOT protect you from area-effect attacks by bosses such as trolls. By the time you get up, your Evasion will usually have expired.

Does NOT always protect you from AI reactions. For example, the AI for trolls typically has them react to attacks from the rear by half-turning back, then whirling around to sweep with their weapon. They will do this even if you are supposedly hidden by Evasion.

In the late game, if you were in front of an enemy and under attack, they will continue to blindly attack you when you go into Evasion. This happens with the dual-wielding humans in the Gray Mountains and Carn Dum. If you move out of the way, they don't automatically follow.

Get this. It is apparently not linked to having Evasion active, and getting to critical strikes faster is better.

Respite - Enables automatic Health and Power regeneration while Evasion is active.

Max this and Evasion duration, and the Power regeneration can easily pay for your use of this Evasion. But maximize it only after getting Elusive Foe, since any attack would otherwise cancel Evasion and your Respite.

Particularly useful starting in the mid-game because an AI-controlled Andriel will start using Wrath of the Eldar aggressively. Any healing Sanctuary that she throws up might not last long enough to be useful because she will spend it with Wrath of the Eldar to hit multiple enemies close by. The problem is, when you need healing, typically you will have a lot of enemies nearby already, or they will follow her to you.

Smoke and Flame - Enhance Evasion by disappearing in a flash that stuns enemies.

Theoretically useful, but the duration isn't very long until you get more ranks, in which case it can last a few seconds. Very good if your allies are already at range, as it gives them free hits. And if you also have Elusive Foe, you can get a lot of multi-target swings in while the enemy is packed together and stunned.

Stealth Mastery - Increase the duration of the Evasion bonus.

Definitely get this, but not before Elusive Foe.

Elusive Foe - Allows you to use normal attacks while Evasion is active without being revealed.

Enter this mode AFTER getting Hero Mode.

Don't cancel your Evasion by using a power or heavy attack while this is active. Just get in as many free hits as possible, and then lay about you with critical strikes once it expires.

Great against trolls and other bosses as they just walk away from you.

Ranger Strike - A quick attack that strikes a single target for bonus damage.

Only slightly faster than a heavy attack. Swings straight down instead of slightly at an angle, so it's slightly harder to hit. Try not to be angled or you might actually miss. You can also confirm a hit first with a heavy attack before following up with this.

Doesn't have the lengthy animation that leaves you vulnerable after.

Doesn't count as a critical strike on an eligible target. I would go with a critical strike over this, then follow up with this to build a second critical strike which usually results in a Sever (and kill).

Dual Wield - Unlocks Dual-Wielding of 1-Handed Weapons and increases the damage done with them equipped.

To progress down the Ranger Strike tree you must choose at least one rank of this or Heavy Weapons. I recommend at least one rank of this. You can almost always buy two one-handed weapons that will net more damage than a two-hander. However, two-handed weapons have more reach, which definitely makes up for it.

Before committing to either Dual Wield or Heavy Weapons, consider whether you can handle one-handed weapons well or not. Remember that you must get closer to a creature to use 1-handed weapons, and you will definitely notice the difference when fighting something like a troll.

It's much more convenient with 2-handed weapons because of the reach, and against normal-sized opponents it's easier to score multiple-targets-hit swings. Against a troll, you must attack from the front or the rear. From the side, you can be pressed right up against its arm but score no hits. When you fight the Spider Queen, you must go from the side, or actually roll *into* her to strike at her centre.

The reach of a two-handed weapon also means you typically get first strike, and that means you can more reliably keep minions in your forward arc away from you and neutralized because you can hit them a second time before they recover from the hit reaction from the first stroke. For slightly more damage per swing, you are also reducing the number of enemies you engage per swing by at least 1 when you choose 1-handed weapons.

Each swing of two weapons inflicts damage from Strength only on the first weapon swing.

Some orcs in the Ettenmoors use this against you and it is devastating as it forces you to block. You can't do anything else fast enough because they keep hitting you and keeping you in the hit reaction. You can do the same to enemies, BUT it doesn't work as well for you for many reasons:

You are almost always outnumbered, so enemies can afford to block all day. You must break their block with a heavy attack.

Large enemies (not just bosses like trolls, but some of the bigger orcs, like the dual wielders and shield bearers in the Ettenmoors) do not suffer severe hit reactions and cannot be kept unbalanced in the same way.

Since you are scoring two hits, each swing increases your Hit Streak by +2, which can translate into a lot of XP. Watch the fun when you fight Bagrisar and accumulate a Hit Streak of 80x or more!

Another interesting application of Dual Wield happens when you get nice weapon properties, such as the Caver's Shortsword (which you can find in the Barrow-Downs, typically near the first town portal, either in the store or in the chest on the nearby hill accessed by a winding path). A Caver's Shortsword shortens your power cooldown time by 11%, so two swords shortens it by 22%. Since you will likely switch weapons quite quickly as you find better ones, this perk of Dual Wielding is of typically of fleeting benefit.

If you maximize skills that improve Evasion duration, AND you get a pair of Glede axes from Nordinbad (-14% skill cooldown time EACH), you can *almost* use Elusive Foe Evasion *constantly*. Having the ability to strike foes unopposed, especially the big ones and bosses to set them up for Critical Strikes, is incredibly powerful and useful.

Combat Training - Increases the damage of your Ranger Strike.

If you don't want to limit yourself with either Dual Wield or Heavy Weapons, then take this.

Heavy Weapons - Increases your damage when wielding 2-Handed Swords.

Damage bonus looks like a small percentage of the weapon damage. Not big enough to really warrant taking this skill unless you have nothing better.

Dual Strike - Attack enemies all around with both weapons. Requires Dual Wielding.

Blood of Westernesse - Reduces the cooldown times of active skills.

Great for keeping up Evasion, especially when having Respite can make it nearly free to use.

Might of the Dúnedain - Each killing blow grants a temporary Strength bonus.

This is easier to use than you think as raw weapon damage starts to wipe out minions even before you can set them up for a critical strike. But I wouldn't prioritize it above filling out key powers under Evasion.

Great to use in the second half of Mirkwood because the small spiders are typically quite easy to kill even without having to use critical strikes.

An okay power for breaking out of a mob without getting out of your defensive stance. Safer than dodging out since blocking is faster and you don't have to drop your block here.

It's better to use dodge and not put yourself in tough spots rather than use this power.

Agility - Grants a bonus of Armor based on your current Dexterity.

A long way to go just to get an Armor bonus. If you are an archer and therefore have invested in a fair amount of Dexterity, then you might as well get this, although blocking and dodging are more foolproof than taking less damage.

Heavy Shot - Hold and release to fire an arrow with greater power.

The crosshair contracts when this power is ready. Has significant knock-back.

This can be a tricky power to use to full potential because you can't make a critical attack with a bow, so to fully benefit from this power you need to be in or near melee. If you are aiming (switched to a bow), and an enemy is too close, you cannot shoot. Instead, you push them back (for no damage).

Precision Aura - A shared bonus increases the damage each party member inflicts with headshots.

Check the stats on how often the AI scores a headshot. Useless waste of points.

Generally the nearest target gets turned into a porcupine. Great for quickly emptying your quiver, but also quickly taking down one minion. Might be useless against really tough opponents such as trolls.

You don't have to aim, so it might be useful if you just want to make a quick "shotgun blast".

I recommend using this against mini-bosses and bosses since you can easily put out over 1000 damage in one go.

Makes every arrow count a lot more, and Heavy Shot already does quite a bit of damage. I'd choose this over Volley.

Character Build
Even if you try to play a ranged character, you will have to deal with melee, and with minions swarming you all the time, it's hard to avoid having a lot of melee action. If you control Eradan, I recommend a melee build. Raise Stamina and Willpower slowly, adding points to it to use gear if you can't get enough stat boosts from items to qualify. Ignore Dexterity unless you really want to play an archer. You will miss out on powerful bows without Dexterity-enhancing items, but you're in melee so much anyway. Maximize Strength while keeping a few points left over to bump up Stamina or Willpower for interesting armor, amulets, or rings.

For skills, head for Elusive Foe as soon as possible, then start extending the duration of your Evasion through Stealth Mastery and Blood of Westernesse. In between I recommend Critical Wound and Respite.

Stay in Evasion as often as possible unless you really don't need to. The nice thing about a melee Evasion Eradan build is Farin will occupy the enemy while you get in your free hits from behind and help him that way. And no one tries to block if you attack from the flank or rear because they can't see you. Grotesquely powerful if you are in Hero Mode.

After getting the skills you want from the Evasion tree, go for Blood of Westernesse and Might of the Dúnedain.